1. Field of the Invention
The present invention relates to an electronic camera and a control program thereof.
2. Description of the Related Art
Images obtained with an electronic camera may sometimes have punctiform shadows which occur due to minute flows on an optical device surface or foreign material such as foams or air bubbles formed inside the optical device. If the foreign material occurs at a place close to an image sensor such as an optical filter disposed on the image pickup plane of the imaging sensor, it has a great influence on an image, and the closer to the image sensor the place of occurrence, the greater the influence on an image.
The foreign material is mainly formed at the time of manufacture of the optical device, and it will not move with time (hereinafter to be referred to as unmoving foreign material). The foreign material of this kind is one of the factors which lead to degrading the performance of the electronic camera.
Generally, the electronic camera uses an optical device which is manufactured by a very advanced manufacturing technique to prevent the foreign material from occurring. However, even if the electronic camera adopts an optical device having the unmoving foreign material, it is able to find them at pre-shipping inspection. Accordingly, the manufacturers of the electronic camera should program the electronic camera in advance in such a manner that signals affected by the unmoving foreign material are automatically corrected so as not to affect generated images. Such programming is a general practice for an image sensor with defective pixels (disclosed in Japanese Unexamined Patent Application No. Hei 5-68209 and so on).
Further, there is another kind of foreign material aside from the above unmoving foreign material. It may possibly occur after shipping of the electronic camera and move over time (referred to as moving foreign material hereinafter). The moving foreign material is a fleck of dust or impurities entering into the camera and attaching to a surface of the optical device or floating in an imaging light path. They are likely to occur especially at exchanging the lens of the electronic camera of lens changeable type. At which place this moving foreign material will occur is unpredictable; therefore, it is not possible to program the electronic camera before the shipping to prevent the occurrence of the moving foreign material. The moving foreign material cannot be found until a user of the electronic camera obtains an image and displays it on the monitor. Consequently, the user needs to perform image correction by himself in order to suppress influence of the foreign material on the image. Specifically, the user has to check the image on the monitor, find out where the foreign material occurs, and designate every found material by use of a computer's graphic software or the like. Besides, the prevention of occurrence of the moving foreign material is very difficult unlike the unmoving foreign material.
In other words, the user has to frequently clean up the inside of the electronic camera with meticulous care and remove dust and impurities causing the moving foreign material. However, it is impossible to remove every fleck of dust despite of however carefully the user handles the camera. Also, there are certain places inside the electronic camera which the user cannot clean up because of the arrangement of the optical device.